1. Field of the Invention
The present invention is directed to exhaust systems and more particularly to a corrosion resistant sound deadening exhaust system.
2. Description of the Prior Art
It is well known in the prior art that the exhaust system of a truck or motor vehicle is frequently subject to failure before other components of the drive system. The exhaust systems are generally exposed to the environment and since they function at elevated temperatures, they are particularly susceptive to corrosion. Generally, most exhaust systems utilize metallic pipes and shells and are susceptible to transmission of exhaust noise to the atmosphere.
The Environmental Protection Agency has recently suggested noise control regulations, that restrict the decibels that a truck can produce. For example, EPA regulations have been proposed, which will require interstate trucks to meet a maximum noise level, when measured at a distance of 50 ft, of 90 decibels at speeds of thirty five miles per hour or less, 88 decibels at speeds over thirty five miles per hour and 86 decibels during a stationary engine run up test. Further, proposed regulations will require new medium and heavy truck noise emissions to be held to seventy five decibels by 1983 with noise measurements being made at a distance of 50 ft from the center line of a test track during a low speed, high acceleration test. It has been estimated that the cost involved in modifying a heavy duty diesel truck to meet these Environmental Protection Agency regulations will be greater than $1,000.00 per truck.
In addition to the Environmental Protection Agency's regulations, states have recently enacted relatively severe noise limitations both with regard to exterior noise and also with regard to the interior cab noise level for the operator.
Various attempts have been utilized in the prior art to limit noise in a truck, for example, manifold exhaust pipes have been wrapped in fiber glass and asbestos for quelling noise. The Plummer U.S. Pat. No. 3,233,699 discloses an exhaust gas muffler tail pipe assembly for a car that is wrapped in a fiberless insulating material with a flexible outer plastic skin.
The Audette U.S. Pat. No. 2,990,906 discloses an acoustical absorber wherein glass fiber is used in combination with a perforated cylinder to optimize the flow of a fluid medium with regards to the creation of turbulent noise. The Fairchild U.S. Pat. No. 844,669, Loomis U.S. Pat. No. 674,210 and Coles U.S. Pat. No. 929,656 are all cited of interest to disclose cylindrical muffler members having an outer steel or aluminim shell and an inner asbestos or mineral wool layer.
There is still a demand in the prior art to provide an effective but economically manufactured noise reduction system to limit the noise produced by a conventional truck engine.